1. Field of the Invention
The present invention relates, in general, to methods and structures for reproduction of sound, and more specifically to the application of acoustic and psychoacoustic principles in the design of an in-ear headphone or in-ear loudspeaker system and to structures incorporating such design principles.
2. Discussion of the Prior Art
One of the most convenient and popular speaker solutions for portable personal audio is the use of in-ear headphones. These headphones can provide exceptional sonic performance and since they can be made to be both light and secure in the listener's ears, provide great convenience, especially for a physically active listener. One type of in-ear headphone, sometimes called “canal phones”, is meant to be placed into the listener's ear canal. They have soft tips surrounding a sound emitting aperture which is oriented in the ear canal towards the tympanum, and are intended to provide a comfortable yet complete acoustic seal between the sound emitting aperture and the outside environment (as illustrated in FIGS. 1-6). This arrangement enhances the perceived acoustic performance of the canal phones and provides exceptional acoustic isolation from the surrounding environment, which is desirable for listening.
One difficulty encountered with such prior art canal phones is that isolation from the surrounding environment is not helpful in many situations, because the listener may have to remove at least one canal phone in order to hear ambient sounds or to communicate with others. Furthermore, positioning the canal phones properly in a listener's ears requires care in order to achieve both comfort and a good acoustic seal for maximum listening performance. Improper positioning of a canal phone can cause ear fatigue or even pain when worn for several minutes or more. Typically, manufacturers provide multiple types and sizes of soft canal phone tips so the listener can select a specific soft tip to find the best fit. The listener or user will typically need to spend some time trying to fit a canal phone comfortably within his or her ear canal, and the insertion and fitting process for finding the best comfort, acoustic isolation and sound quality often requires pushing on the canal phone, pulling or tugging on the ear and removing and re-inserting the canal phone. Then, once the listener has obtained a satisfactory fit for the canal phone, he or she does not want to remove it and then have to go through the insertion and fitting process again, but the user may need to hear something or someone. As a result, the acoustic isolation from a properly fitted canal phone frustrates a listener who may momentarily want to hear something or someone.
Others have developed audiologist's products (such as hearing aids) which permit an “ear-plug” structure to be adapted in a manner which allows some sound from the environment to pass into the ear canal. Musicians who perform music styles noted for their loud nature, especially rock music, often wear earplugs to prevent their own performances from damaging their hearing. Musicians' earplugs are designed to attenuate sounds evenly across the audio band and thus minimize their effect on the user's perception of bass and treble levels. These are commonly used by musicians and technicians, both in the studio and in concert, to avoid overexposure to high sound pressure or volume levels. Musicians' earplugs typically include a central tubular body with an open interior lumen, a proximal end adapted to fit within the ear canal and a distal end which projects outwardly to give the user something to grasp and manipulate. The distal end of the tubular body can be open to the environment or closed and can define an acoustic transmission line with a damper or attenuator at the closed distal end. The tubular body's proximal end carries one or more compliant, rubbery domed flanges shaped to form a seal in outer part of the ear canal. The proximal end of the tubular body defines a sound output port or small hole at the proximal end of the plug, so attenuated sound can pass into the ear canal. However, such earplugs are not suitable for listening to high quality recorded sound unimpeded by ambient noise.
Other devices which permit a user to hear at least some ambient sound include safety equipment which incorporates active electronics either to cancel environmental sounds or to allow the listener to hear them, but such devices require the use of microphones, amplification, noise filtering/canceling circuits and power that must be provided either from the source electronics or batteries. These requirements create additional cost, bulk and inconvenience.
Headphones known as ear-buds are also available (see, e.g., FIG. 3a and FIG. 5). These sit in the lower pinna portion of the ear, and are typically fitted to the listener by having the larger portion of the ear-bud in the listener's lower concha, sometimes called the cava, between the tragus and anti-tragus portions of the ear. But ear-buds typically do not fit snugly in the ear canal when positioned according to the manufacturer's instructions, and do not create an acoustic seal. Therefore, they do not create much acoustic isolation and always allow passage of a significant amount of environmental sound.
There are also headphones known as supra-aural headphones. These typically allow the passage of more environmental sound to the listener via leakage because they do not produce a particularly good seal to the listener's ear. Unfortunately, this also often results in poorer acoustic performance of the headphones and, since the leakage cannot be switched off, the listener typically cannot eliminate this distraction at appropriate times nor achieve optimum acoustic headphone performance.
There is a need, therefore, for a convenient, flexible, inexpensive and unobtrusive earphone structure and method for selectively passing or blocking environmental ambient sound, while permitting the user to enjoy high fidelity or “audiophile” quality sound playback.